Sport balls, such as basketballs, and the like, contain hollow rubber bladders, the production of which involves a rather complex process. For example, rubber compounds, such as butyl rubber, are compounded on a rubber mill or a Banbury mixer and the compound is calendered to the desired thickness in sheet form. Quarter sections are then die cut from the rubber sheet and pieced together by hand and end patches. A valve is then inserted and adhered to the construction which is then heat cured to produce an inflatable bladder. Because of the adhesive splices, imperfect seals and poor weight balance, high numbers of defective bladders and excessive waste material often result.
In order to overcome these difficulties, the industry now employs a rotocasting process, involving a thermoplastic material such as polyethylene or a vinyl plastisol. However, these materials do not have the resiliency and air retention of rubber and have not proved suitable for use in basketballs, and the like. It has been proposed to employ in the rotocasting process liquid carboxy-terminated poly(butadieneacrylonitrile)polymers, as described in U.S. Pat. No. 4,119,592, issued Oct. 10, 1978. These polymers proved to be very effective in producing rubber bladders for sport balls.
In all of the processes used heretofore, it has been necessary to build dimensional stability into the product. Without some means of dimensional reinforcement, inflated elastomeric sport balls gradually grow in size and become unsuitable for proper use. Presently, the industry employs a filament winding process using nylon filaments, for example, to reinforce the bladder component of sport balls. However, the filament winding process is quite complicated and usually requires computerized controls in order to achieve uniformity of distribution. Further, the winding operation is a separate step following the production of the bladder component which not only complicates the process of producing rubbery bladders but also increases the cost of producing sport balls. Accordingly, there is a need in the art to simplify the process of producing rubbery bladders for pneumatic sport balls or playballs.